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Amiga Hardware Issues and discussion / Re: I made a modified accelerator, it works, but has a problem
« Last post by SpeedGeek on April 20, 2024, 03:29:07 PM »Yep, exactly half reported by ATK. With the unmodified accelerator at 14MHz it reports a reasonable 59.83Hz. Interestingly SysInfo measures the correct 60 unlike ATK, presumably using a different timer. At 21MHz ATK measures some even crazier number like 39Hz. So the faster it goes the lower vblank frequency it measures.
That is my understanding.
Something I hadn't tested up until this point, I had KS 1.3 ROM in there this whole time, because 500 rev.5 has the oopsie mistake on the board, I finally installed and wired up correctly the KS 3.1 ROM, and unlike 1.3 this one does not boot from the Gotek floppy at either 21 and 28MHz... So that's a newly discovered problem #2, though very high likelihood it is related to the same interrupt/timer problem. Obviously I will need to revert to KS 1.3 ROM to run ATK for further testing until these interrupt timers are ironed out.
I feel like I'm so close... Just wish I knew what rogue signal causes the speedup.
Did you forget about the E clock? All 68000 CPU based Amigas use the E clock generated by the CPU. So with a 14 MHz CPU clock you should divide the E clock by 2 and a 28 MHz CPU clock divide it by 4.
Don't mess with odd asynchronous clock frequencies unless you have the extra logic to generate the proper E clock. This is exactly what the 68020+ CPU based Amigas do.
